The present invention relates in general to thermal ink jet (TIJ) printheads and more specifically to a large array printhead having a large array of TIJ thin-film ink drop generators formed on a single monolithic substrate.
Thermal ink jet (TIJ) printers are popular and common in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of OUTPUT HARDCOPY DEVICES (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. Ink jet printers produce high-quality print, are compact and portable, and print quickly and quietly because only ink strikes a print medium (such as paper).
An ink jet printer produces a printed image by printing a pattern of individual dots (or pixels) at specific defined locations of an array. These dot locations, which are conveniently visualized as being small dots in a rectilinear array, are defined by the pattern being printed. The printing operation, therefore, can be pictured as the filling of a pattern of dot locations with dots of ink.
Ink jet printers print dots by ejecting a small volume of ink onto the print medium. These small ink drops are positioned on the print medium by a moving carriage that supports a printhead cartridge containing ink drop generators. The carriage traverses over the print medium surface and positions the printhead cartridge depending on the pattern being printed. An ink supply, such as an ink reservoir, supplies ink to the drop generators. The drop generators are controlled by a microprocessor or other controller and eject ink drops at appropriate times upon command by the microprocessor. The timing of ink drop ejections generally corresponds to the pixel pattern of the image being printed.
In general, the drop generators eject ink drops through a nozzle or an orifice by rapidly heating a small volume of ink located within a vaporization or firing chamber. The vaporization of the ink drops typically is accomplished using an electric heater, such as a small thin-film (or firing) resistor. Ejection of an ink drop is achieved by passing an electric current through a selected firing resistor to superheat a thin layer of ink located within a selected firing chamber. This superheating causes an explosive vaporization of the thin layer of ink and an ink drop ejection through an associated nozzle of the printhead.
High speed printing systems, such as large format devices and drum printers (which print on a large scale, for example, architectural drawings), use a large array printhead containing arrays of ink drop generators in order to print over a wide area. In general, a large array printhead is preferably defined as greater than 1 inch in extent. Large array printheads have been conceived that embody multiple thermal inkjet substrates that are aligned and attached to a carrier substrate. For example, U.S. Pat. No. 5,016,023 discusses separate silicon thin films formed as TIJ thin-film substrates. However, one problem with this type of large array printhead is that the TIJ thin-film substrates must be mechanically aligned to the carrier substrate, which is costly and may result in inadequate relative alignment between drop generators on the separate substrates.
Thus, there exists a need for a dimensionally precise large array printhead suitable for high-speed printing systems wherein the size of the substrate is not limited. Moreover, there is a need for an inexpensive large array printhead having a single monolithic substrate, so that the carrier substrate is the TIJ substrate and the expense and difficulty of aligning multiple substrates are eliminated.
To overcome the limitations in the prior art as described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a large array printhead having a large array of ink drop generators formed on a single monolithic substrate. The present invention provides an inexpensive large array printhead that uses a single monolithic substrate so that the need to align multiple substrates is alleviated. Moreover, the single monolithic substrate is made from a suitable material so that the size of the substrate is not limited.
The large array printhead of the present invention includes a large array of ink drop generators that are formed on a single monolithic substrate. The printhead includes a driver device circuit (preferably a multiplexing device) that reduces the number of incoming leads to the ink drop generators and decreases the parasitic resistance of the printhead. Preferably, the multiplexing device is on the back of the substrate so that it does not interfere with the printing operations on a print media. The ink drop generators are a layered thin-film structure formed on the substrate using thin-film techniques. These layers include a resistor layer, for heating ink from an ink source to a high temperature to cause an ink drop ejection and a barrier layer, for providing necessary structure to form a firing chamber and ink feed holes, which provide ink to the resistor. These layers also include an orifice layer that contains a nozzle from which the ink drop is ejected. Another embodiment of the invention includes a barrier layer having a plurality of ink feed holes and another embodiment includes a large array printhead having a plurality of chambers that may contain different ink colors.
The present invention is also embodied in a plurality of techniques that are used fabricate the above-described large array printhead. These techniques include etching and patterning the layered thin-film structure on the substrate. In a preferred embodiment, the substrate is etched and patterned first and then the multiplexing device is attached at a later time. Attachment may be accomplished using a several techniques including soldering the device to the substrate. Moreover, flat panel techniques and equipment may be used to fabricate the large array printhead of the present invention.